Use in combination with levodopa: Usual range: 3 to 6 mg/day in divided doses

Usual Pediatric Dose for Cerebral Spasticity

Oral:
Children 2 to 17 years old:
Dystonia in cerebral palsy:
Initial: 0.1 to 0.2 mg/kg/day in three divided doses for 1 week; increase by 0.05 to 0.3 mg/kg/day in three divided doses for the second week; thereafter, titrate up weekly by 0.05 to 0.5 mg/kg/day in three divided doses as clinically tolerated
Maximum dose: 0.75 mg/kg/day

Renal Dose Adjustments

Due to a lack of pharmacokinetic data, there are no guidelines available for the dosing of trihexyphenidyl in patients with renal disease. If trihexyphenidyl is needed in this patient, therapy should be initiated with a low dosage and titrated conservatively. This patient may also be more sensitive to the anticholinergic effects of trihexyphenidyl and should be monitored closely.

Liver Dose Adjustments

Due to a lack of pharmacokinetic data, there are no guidelines available for the dosing of trihexyphenidyl in patients with liver disease. If trihexyphenidyl is needed in this patient, therapy should be initiated with a low dosage and titrated conservatively. This patient may also be more sensitive to the anticholinergic effects of trihexyphenidyl and should be monitored closely.

Precautions

Trihexyphenidyl has cumulative effects. Therefore, continued supervision of the patient is recommended.

Trihexyphenidyl may impair mental and/or physical abilities. Patients should be cautioned about driving or operating dangerous machinery. The elderly may be particularly vulnerable to these effects.

Anticholinergic agents, including trihexyphenidyl, are not effective in controlling tardive dyskinesia (TD) and in some cases may aggravate it or induce previously suppressed symptoms. Trihexyphenidyl should be avoided in patients presenting with TD. If TD symptoms develop or worsen during treatment with trihexyphenidyl, prompt withdrawal of therapy will provide better chances of improving the condition.

Trihexyphenidyl should be used cautiously in patients with cardiac disorders, including a tachycardic tendency or hypertension, liver disorders, kidney disorders, prostatic hypertrophy, obstructive disease of the gastrointestinal or genitourinary tracts, or angle-closure glaucoma. Patients should have intraocular pressures checked at regular intervals.

Abrupt discontinuation of long-term trihexyphenidyl therapy may be associated with withdrawal and cholinergic rebound symptoms, including myalgias, diaphoresis, gastrointestinal distress, lethargy, depression, anxiety, tachycardia, orthostatic hypotension, hallucinations, and relapse or exacerbation of extrapyramidal effects. Withdrawal symptoms may be delayed by days to weeks after stopping medication.

Due to its hallucinogenic and euphorigenic effects, trihexyphenidyl is subject to potential misuse by drug abusers.

Since the use of trihexyphenidyl may, in some cases, continue indefinitely and since it has atropine-like properties, patients should be subjected to constant and careful long-term monitoring to avoid allergic and other untoward reactions.

Geriatric patients, particularly over the age of 60, commonly develop increased sensitivity to the actions of drugs of this type, and hence, require strict dosage regulation.